1. Field of the Invention
The invention relates to energy storage devices, and more particularly to an improved rotatable mass for an energy storage device adapted to be employed as a flywheel.
Because of the so-called energy crisis, renewed interest has been experienced for energy storage devices capable of storing energy obtained at low costs for use under different conditions at later periods of time.
As discussed in Scientific American, December, 1973, Volume 229, No. 6, flywheels are notoriously old and have long been used for storing energy. However, until recently it was thought that the use of flywheels was severely limited due to factors including weight of the rotatable mass forming the rotor, and fabrication costs.
As is well known, the amount of energy which can be stored in a flywheel depends largely upon the weight of the rotatable mass and the angular velocity at which the mass is caused to spin. The limit of the amount of energy which can be stored in the rotatable mass of a flywheel ultimately is determined by the tensile strength of the material from which the mass is made.
2. Brief Description Of The Prior Art
It has been suggested that the materials most suited for use in fabricating a rotatable mass for a flywheel are characterized by low density and high tensile strength. Recently, efforts have been directed to developing rotatable masses for flywheels from such materials. The results of such efforts are typified by the devices described in the disclosures of U.S. Pat. Nos. 3,296,886, 3,788,162and 3,859,868.
However, those engaged in the design of flywheels continue to be plagued by the destructive effects of stress, both tangential and radial, which results from angular velocities operatively imposed on flywheels. For example, flywheels having a solid mass of thick-ring configuration, formed from circumferentially wound glass fibers, embedded in an epoxy, fail at speeds far below the limit set by the tensile strength of the fibers. Usually, this is because of progressively worsening radial delamination within the rotary masses of the flywheels.
Additionally, where a flywheel mass is mounted on a shaft extended through an opening formed therein by removing materials from the center of the mass, the flywheel is subject to failure, due to the resulting stresses in the zone immediately adjacent to the opening formed by the removal of the materials. In instances where fibers are arranged in parallelism and then bonded together for forming a disk-shaped rotary mass, in a manner such that the fibers lie along cords of the mass, the flywheel is subject to failure during high speed operations, for substantially the same reasons as are flywheels formed from circumferentially wound glass fibers, as hereinbefore discussed.
It is, therefore, apparent that even though substantial efforts have been made to improve rotary energy storage devices by fabricating the rotatable masses of such devices from fibers characterized by low density and exhibiting high tensile strength characteristics, further advances in the design and fabrication of rotatable masses for energy storage devices are highly desirable, or even necessary, in order to enhance the adaptability and use of such devices in the continuing effort to acquire a solution to the problem of efficiently utilizing available energy.
It is, therefore, the general purpose of the instant invention to provide an economic and practical rotatable mass for a flywheel which is characterized by increased energy storage capabilities and an operational life of increased duration.